This invention relates to an array substrate for flat-panel display devices and, more particularly, to an array substrate having inspection pads as well as connection pads for mounting driver circuit at periphery of the substrate.
Recently, flat-panel display devices such as liquid crystal display devices have been used as image display devices for television set, various computers, car navigation system and the like because of their features that they are thin and light-weighted and consume a small electric power.
A flat-panel display device such as a liquid crystal display device is comprised of an array substrate having pixel electrodes and a pixel-driving wiring pattern thereon and a counter substrate assembled with the array substrate. A liquid crystal layer acting as a light modulating layer, for example, is held between the array and counter substrates. The array substrate generally has a pixel area for displaying an image and a peripheral connection area at outside of the pixel area, on an insulating substrate plate that comprised the flat-panel display. On the peripheral connection area, driver circuits and input wirings are disposed.
In a so-called chip-on-glass (COG) method as a way for disposing the driver circuits on the peripheral connection area, driver IC chips are directly mounted on an insulating substrate such as a glass plate using connecting means such as anisotropic conductive film (ACF). This COG method enables not only size reduction of non-displaying peripheral area of the display panel but also cost reduction for parts and assembling process of the flat-panel display devices.
Processes for manufacturing flat-panel display devices often include an inspection process for detecting any defect such as short-circuiting, pixel defect and display unevenness in the array substrate, prior to the process for mounting the driver IC chips. This inspection process is needed in many case because mounting of the driver IC chips on a defective array substrate not only makes the mounting process in vain but also causes damage on the driver circuits when the driver IC chip is peeled off.
In case of manufacturing active-matrix liquid crystal display devices using thin film transistors (TFTs) as pixel switching elements, the inspection process also reveals disconnection in signal lines and scanning lines and short-circuiting between the signal and scanning lines at their crossing points as well as defects of the TFTs.
For implementing such inspection process, inspection pads for contacting with inspection probe (tester probe) of inspection apparatus have to be disposed respectively to each of signal-input wirings at the periphery portion of the array substrate.
JP-A-1989-296103 (JP-A-11296102, or Japanese patent publication unexamined No.11-296102(1999)) proposes a rectangular array substrate having inspection pads for the signal lines at along the edge opposed to an edge along which signal-line driver IC chips are disposed. The inspection process is facilitated by such construction of the array substrate.
However, sizes of periphery area for external connection become large as much as sizes of an area for disposing the inspection pads. In this way, sizes of non-displaying area (picture-frame area) become large at periphery of the flat-panel display. Size increase of the non-displaying area may be avoided by removing the area for the inspection pads after the inspection process. Even in this case, there arises decrease in number of array substrates obtainable from one gang-printing substrate.